Transport networks are for example networks based on SDH (Synchronous Digital Hierarchy) as defined in ITU-T G.707 12/2003 or OTH (Optical Transport Hierarchy) as defined in ITU-T G.709 03/2003. These ITU-T recommendations are both incorporated by reference herein. Such transport networks have a multi-layer multiplex hierarchy where higher layer transport signals serve for the transport of either tributary signals or lower layer transport signals, which can then transport tributary signals at a lower rate. A higher layer is thus referred to as a server layer and a lower layer as a client layer.
For example in SDH, a transport frame is called STM-N (N=1, 4, 16, 64, or 256) and can transport N entities referred to as virtual containers VC4. A VC4 can either carry a 140 Mbit tributary signal or a number of lower order virtual containers VCn (n=11, 12, 2, 3). Accordingly, a connection utilizing VC4 is in SDH termed a higher order path (HOP) connection and a connection utilizing VCn (n=11, 12, 2, 3) is termed a lower order path (LOP) connection. A HOP is thus a server layer to a LOP as client layer. More generally, a VC4 is also referred to as a higher order VC (HOVC), a term which applies also to the North American SDH equivalent named SONET, i.e. to a SONET VC3 and also to a concatenation of VC4 (or SONET VC3), i.e., VC4-xc, x=4, 16, 64.
In OTH, which is based on wavelength division multiplexing of optical wavelength channels, there exist multiplex entities termed optical channel data units ODUk with k=1, 2, or 3. An ODU1 can be transported in an optical channel OCH with a bandwidth of 2,5 GBit/s or four ODU1 can be multiplexed into an ODU2, which is then transported in an optical channel OCH with a bandwidth of 10 GBit/s. Hence, the ODU2 is a server layer to an ODU1. Moreover, an ODUk can transport an SDH STM-N of suitable size. Therefore, ODUk can be a server layer to STM-N.
While transport networks like SDH and OTH networks are still based on circuit switching technology, routing algorithms are implemented to dynamically setup and release connections as these may be required. Such dynamic connections are well suited for the transport of packet switched traffic such as Ethernet, ATM, or IP. Accordingly, to make the transport networks “data-aware”, a new routing protocol termed GMPLS (Generalized Multiprotocol Label Switching) has been defined in the IETF. GMPLS supports not only devices that perform packet switching, but also those that perform switching in the time, wavelength, and space domains. For this purpose, network elements in the transport network are equipped with GMPLS routing extensions, i.e., a distributed control plane composed of GMPLS controllers, which communicate among each other via a dedicated control network (typically an Ethernet) and automatically provision new connections by configuring their respectively associated network elements to switch the respective connection.
However, GMPLS routing mechanisms work only on a single network layer. In a multi-layer transport network, a request for a client layer connection can only be served if server layer connections exist that can be utilized. Extensions towards multi-layer e.g. for Ethernet over SDH are currently under discussion but require complex interactions on control plane level. This creates communication overhead and leads to complex recovery scenarios.
The unpublished European Patent Application 05291164 filed on 30.05.2005, which is incorporated by reference herein, describes a routing method and related network management system, which take into account more than one network layers. However, since in this solution server layer connections are automatically set up to provide client layer connections, the influence the operator can take on the routing in the network is limited and his capabilities of traffic engineering are reduced.
It is therefore an object of the present invention to provide a method and related control plane for automatically provisioning connections in a multi-layer transport network, which creates less overhead and allows to use the network resources more efficiently.